Effect of salinity stress on the life history variables of Branchipus schaefferi Fisher, 1834 (Crustacea: Anostraca)

BACKGROUND: Freshwater anostracans inhabit ephemeral water bodies in which as the water level decreases due to evaporation the salt concentration increases. Thus, for most anostracans salinity becomes the major stress factor. RESULTS: We tested five concentrations of NaCl (0 to 8 g/l) on the life table demography of Branchipus schaefferi fed Chlorella (alga). Age-specific survivorship curves of male and female B. schaefferi showed nearly a similar pattern in that increased salt concentration resulted in decreased survivorship. The age-specific reproduction (m(x)) of females showed several peaks of cyst production at 0 and 1 g/l salinity while in treatments containing salt at 4 or 8 g/l, there were fewer peaks. Average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase were all significantly influenced by the salt concentration in the medium. The highest value of net reproductive rate (970 cysts/female) was in treatments containing 0 g/l of salt, while the lowest was 13 cysts/female at 8 g/l. The rate of population increase (r) varied from 0.52 to 0.32 per day depending on the salt concentration in the medium. CONCLUSION: The low survival and offspring production of B. schaefferi at higher salinity levels suggests that this species is unlikely to colonize inland saline water bodies. Therefore, the temporary ponds in which it is found, proper conservative measures must be taken to protect this species

Rotifers in Lake Orta: a potential ecological and evolutionary model system

Lake Orta experienced for a few decades a unique history of chronic pollution, with extreme changes in pH and copper concentration. Currently, the lake has recovered to its almost pristine oligotrophic conditions, but its sediments still preserve the record of all the changes that happened since the establishment of the first polluting factories in the 1920s, through to the liming activities in 1989-1990, and to the recovery phase that is still going on. Here we review the current knowledge for Lake Orta regarding rotifers, a diverse component of the zooplankton of the lake, through studies on living organisms and on their resting stages accumulated in the sediments. We also report a brief review of what is known in general on the effects of changes in pH and copper concentration on rotifers at the population, species and community level, providing expectations for such effects on the rotifers of Lake Orta. Then, we conclude our review with a perspective on the potential use of rotifers hatched from the resting stages in the sediment of Lake Orta with the description of experiments that can be performed in the future in the framework of resurrection ecology, in order to understand the mechanisms of past and future changes in the environment

Differences in population growth of rotifers and cladocerans raised on algal diets supplemented with yeast

AbstractWe studied the population growth of two rotifer (Brachionus calyciflorus and Brachionus rubens) and two cladoceran (Ceriodaphnia dubia and Moina macrocopa) species fed three diets (Chlorella vulgaris (Ch), Scenedesmus acutus (Sc) and yeast (Saccharomyces cerevisiae) (Y) in seven combinations (alone or mixed in equal proportions (on dry weight basis): Ch+Sc, Ch+Y, Sc+Y and Ch+Sc+Y). In general, the cladocerans were more adversely affected than the rotifers on the diet of yeast alone. The population growth curves of B. calyciflorus and B. rubens revealed that algal diets were superior to yeast. Regardless of diet, B. rubens had a longer lag phase and delayed peak density compared to B. calyciflorus. Both M. macrocopa and C. dubia had higher peak abundances when fed mixed algae than on either alga offered separately. B. rubens, C. dubia and M. macrocopa reached significantly lower maximal densities on diets containing yeast, S. acutus or both. When the data on the eggs/female (egg ratio) were plotted as function of population density, we found an inverse relation, which was curvilinear for B. calyciflorus and linear for B. rubens. In general, we found that yeast could effectively supplement algal diets in all the test species, thereby reducing costs in large scale production of zooplankton

Producción de microcistinas en Microcystis inducida por Daphnia pulex (Cladocera) y Brachionus calyciflorus (Rotifera)

Freshwater cyanobacteria often are the predominant division of phytoplankton in eutrophic environments. Microcystis is a bloom-forming cyanobacterium, commonly found in urban lakes of central Mexico. Several biotic factors including the presence of zooplankton induce the production of toxins (microcystins, MCs) in Microcystis. Here, it present data on the effect of the presence of the cladoceran Daphnia pulex (Leydig, 1860) and the rotifer Brachionus calyciflorus (Pallas, 1776) on total MCs production in Microcystis spp. Results indicate that Microcystis spp. with or without the presence of zooplankton (controls), contained certain level of MCs (1.32 to 3.98 x 10-4 ng/cell). At low cell density of Microcystis spp. (0.5 x 106 cells/mL) and, in the presence of high zooplankton abundance (25 cladocerans or 250 rotifers, in 50 mL), the MCs concentration was significantly higher as compared to controls. Moreover, under low zooplankton density and at low density of Microcystis spp., the MCs levels did not vary significantly. Compared to rotifers, the presence of cladocerans resulted in higher MCs levels. This work demonstrates that zooplankton presence may induce microcystins production in Microcystis spp.Las cianobacterias de agua dulce regularmente son la división predominante del fitoplancton en ambientes eutrofizados. Microcystis es una cianobacteria formadora de florecimientos, comúnmente encontrada en lagos urbanos del centro de México. Diversos factores bióticos incluyendo la presencia de zooplancton inducen la producción de toxinas (microcisti­nas, MCs) en Microcystis. En este trabajo se presentan datos sobre el efecto de la presencia del cladócero Daphnia pulex (Leydig, 1860) y del rotífero Brachionus calyciflorus (Pallas, 1776) en la producción total de MCs en Microcystis spp. Los resultados indicaron que Microcystis spp. con o sin presencia de zooplancton (controles), contiene ciertos niveles de MCs (1.32 a 3.98 x 10-4 ng/cél). A baja densidad celular de Microcystis spp. (0.5 x 106 cél/mL) y con la presencia de altas abun­dancias de zooplancton (25 cladóceros o 250 rotíferos, en 50 mL), la concentración de MCs fue significativamente mayor al compararla con los controles. Además, con una baja densidad de zooplancton y una baja densidad de Microcystis spp., el nivel de MCs no varió significativamente. En comparación con rotíferos, la presencia de cladóceros resultó en niveles altos de MCs. Este trabajo demostró que la presencia de zooplancton puede inducir la producción de microcistinas en Microcystis spp

Cliquer, glisser, dactylographier ou sélectionner dans un menu déroulant : manipulations préférées des étudiants universitaires. Click, slide, type or select in a pop-up menu: Favourite manipulations of French-as-a-second-language university students

Résumé:Cet article présente les résultats d`une recherche sur les préférences d’étudiants universitaires de français langue seconde en ce qui a trait aux différentes manipulations faites lors d’activités de grammaire informatisées. Dans un contexte d’activités à choix multiples, les étudiants ont indiqué leurs préférences envers les quatre manipulations proposées (cliquer, glisser, sélectionner dans un menu déroulant et dactylographier). Nos résultats, appuyés des commentaires des étudiants, démontrent en général que leurs préférences reflètent les caractéristiques des « enfants-roi » qui préfèrent des activités ludiques, faciles et rapides qui nécessitent peu d’investissement de leur part et ont un impact direct sur leurs notes. Abstract This article presents the results of a study on the preferences of French-as-a second-language university students towards different manipulations used in computerized grammar activities. Students indicated their preferences for the four manipulations offered (click, scroll-down menu, drag-and-drop, keyboard entry) while doing multiple-choice activities. Our results, backed up by student comments, show that their preferences reflect the traits of the “spoiled child” who prefers activities that are fun, easy and fast and that will have a direct impact on grades

Effect of algal food (Chlorella vulgaris) concentration and inoculation density on the competition among three planktonic Brachionidae (Rotifera: Monogononta)

Competitive outcomes among three rotifer species (Anuraeopsis fissa, Brachionus havanaensis and B. angularis) were quantified with different inoculation densities of two competing species at a time (0, 25, 50, 75 and100%) and using different algal (Chlorella vulgaris) densities (0.2 × 106 , 0.4 × 106 and 0.8 × 106 cells ml-1). In control cultures, when each species was grown alone, the population growth of rotifers increased with increasing food availability in the medium, but in mixed cultures, decreased with increasing proportion of the competing species. At low food level, compared to B. havanaensis, B. angularis had stronger negative impact on A. fissa. However, with increasing algal density, both species of Brachionus had similar but reduced impact on A. fissa. Population growth of B. havanaensis was more adversely affected by A. fissa than B. angularis at low and intermediate concentrations. At high food level, the impact of either A. fissa or B. angularis on the growth of B. havanaensis was similar. When grown alone, for a given food density, A. fissa was more numerically (4 to 6 times) abundant than the other two species. The rate of population increase (r) of rotifers increased with increasing food levels. Depending on the rotifer species and the test conditions, the r varied from -0.001 to 0.34 d-1. Results showed that the competitive outcome in the tested rotifers depended on the initial inoculation density of the competing species, the offered food concentration as well as the interaction of these two factors

Effects of selected pharmaceuticals (ibuprofen and amoxicillin) on the demography of Brachionus calyciflorus and Brachionus havanaensis (Rotifera)

AbstractThe levels of emerging chemicals have increased dramatically during the last two decades posing problems for human and environmental health. Pain-killers such as ibuprofen and antibiotics such as amoxicillin are generally consumed together and hence are discharged into waterbodies as effluents. The lack of a rigorous control of pharmaceutical discharges into natural waterbodies is a concern for limnologists and ecotoxicologists because of their possible effects on non-target organisms. Rotifers, due to their sensitivity, short generation time and high reproductive rates, are widely used as bioassay organisms in testing the effects of different substances including pharmaceuticals. Here we quantified the demographic responses of Brachionus calyciflorus and Brachionus havanaensis exposed to three sublethal concentrations of ibuprofen (25, 12.5 and 6.25mgL−1) and amoxicillin (200, 100 and 50μgL−1). Our data showed that both survivorship- and reproduction-related variables were negatively affected with increasing concentrations of both pharmaceuticals. The rate of population increase of B. calyciflorus (0.63–0.72d−1) was not affected by amoxicillin or by ibuprofen but for B. havanaensis, it was decreased significantly (from 0.89 to 0.38d−1). Compared to ibuprofen, amoxicillin had more adverse effects on both the rotifer species